This invention relates in general to vehicle disc brake assemblies and in particular to an improved guide pin locating feature adapted for use in such a vehicle disc brake assembly.
Most vehicles are equipped with a brake system for slowing or stopping movement of the vehicle in a controlled manner. A typical brake system for an automobile or light truck includes a disc brake assembly for each of the front wheels and either a drum brake assembly or a disc brake assembly for each of the rear wheels. The brake assemblies are actuated by hydraulic or pneumatic pressure generated when an operator of the vehicle depresses a brake pedal. The structures of these drum brake assemblies and disc brake assemblies, as well as the actuators therefor, are well known in the art.
Typical disc brake assemblies include a rotor which is secured to the wheel of the vehicle for rotation therewith. The rotor includes a pair of opposed friction plates which are selectively engaged by portions of a caliper assembly. The caliper is slidably supported on an anchor bracket by guide pins. The guide pins are secured to the caliper by guide pin fasteners and contact the anchor bracket at contact points. In turn, the guide pin fasteners are secured in caliper bores. The anchor bracket creates a contact load on each of the guide pins at the contact points.
The anchor bracket is attached to a non-rotatable component of the vehicle, such as the vehicle frame. The caliper assembly includes a pair of brake shoes which are disposed on opposite sides of the brake rotor. The brake shoes are connected to one or more hydraulically or pneumatically actuated pistons for movement between a non-braking position, wherein they are spaced apart from the opposed friction plates of the rotor, and a braking position, wherein they are moved into frictional engagement with the opposed friction plates of the rotor. When the operator of the vehicle depresses the brake pedal, the piston urges the brake shoes from the non-braking position to the braking position so as to frictionally engage the friction plates of the rotor and thereby slow or stop the rotation of the associated wheel of the vehicle.
The braking position produces a torque force on the brake assembly. The torque force results from the brake shoes and caliper in the braking position being dragged by the rotor. The torque force causes anchor bracket deflection and brake caliper translation. Anchor bracket deflection occurs when the brake shoes and caliper in the braking position are dragged by the rotor and the brake pads contact an abutment of the brake caliper. The brake pads contacting the abutment causes the anchor bracket to deflect—i.e., the anchor bracket rotates about an attachment point between the anchor bracket and the non-rotatable component of the vehicle. The torque force produces a moment around a mounting bolt securing the anchor bracket to a stationary component of the vehicle. The anchor bracket deflection and the mounting bolt moment results in joint slippage for the fasteners.
Additionally, the deflection and/or translation may increase the contact load between the anchor bracket and the pins sufficiently to bind the guide pins against the anchor bracket. Binding reduces the ability of the caliper to slide and move the brake shoes between the non-braking and braking positions.
It is known to those skilled in the art that the guide pins may be tapered to prevent joint loosening. Joint slippage and loosening are distinct. Joint slippage is when the joint maintains the original clamp load but displaces. Joint loosening is when the original clamp load is reduced, with or without joint displacement. For example, a through bolt may be holding two plates together. If the through bolt shifts within holes through the plates or the plates shift relative to each other, but there is no reduction in the clamping force of the bolt, then there is joint slippage without joint loosening.
Furthermore, the guide pins may be tapered to control an insertion depth of the guide pin into the anchor bracket, as in U.S. Patent Publication No. 2007/0051568.
Thus, it would be desirable to have an improved guide pin locating/mounting feature which reduced bracket translation and caliper deflection.